Get this simple set of ingredients together before you begin.
Remove any remaining pin bones from the fillets with your fingers or tweezers.
Place the fillets skin side down in a shallow bowl and pour the sake over them. Allow the sake to soak in for about 1 minute.
Pat the fillets dry with paper towels and generously sprinkle salt on both sides. Place the fish skin side up and set aside for 20 minutes.
Preheat your oven to 400°F. Line a sheet pan with aluminum foil or parchment paper.
Pat the fillets dry again with paper towels and transfer them to the sheet pan skin side down.
Bake on the lower rack of the oven until fish is just cooked through, approximately 15 minutes. Turn the fish over so that the skin is facing up and bake on the top rack until the skin is golden brown and a little crispy, 2 to 5 minutes.
Transfer the mackerel to a serving platter with a pile of shredded daikon, lemon wedges, and tamari on the side.